I have two excellent put downs......tend to work better in a kebab shop rather than a forum though.

1) guy astarts hurling abuse at you in the queue, you act really timid, then burst into life, pointing straight at him, and yell..... "youuuuuuuuuuuuuuuuuuuuuuuuuu (then pause, its the timing that counts) have a stupid face. "

I saw this used in Boscombe, and it worked a treat. Guy just walked off.

2) 1st guy.... You are one fat motherfucker
2nd guy.....well I can loose weight, you'll always be an ugly cunt.

If all else fails, just piss on your hand and then shake theres, that always seems to work.